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Dear All I have a twinned data with a twin fraction of 0.467549. The resolution of the data is 3Å. I have a molecular replacement solution from phaser and assigned the free R reflections using thin shells in shelxpro. Since I have 4 molecules per asu, I thought that refining it with the NCSY command in shelxl could circumvent the low resolution as suggested in the shelxl manual. I did a rigid body refinment with BLOC 1, AFIX 6 and AFIX 0 (after each chain). TWIN matrix and BASF using LS and removing the BUMP. I get the following : R1 = 0.3850 Rfree = 0.4197 wR2 = 0.7337 for all data. When I do restraint refinement (ie coordinates and isotropic B-factors) using CGLS, removing the AFIX and BUMP, reducing the SIMU, and DEFS values I get a large difference (20) between Rfree and R1 indicating that the data is being overfitted. Using the default values for SIMU and DEFS does not help. Has anybody succeded in refining twinned data to this low resolution with shelxl and how can I get it to work in my case considering that I will use NCS? Thank you all in advance Veronica --------------------------------------------- Tamu Dufe Veronica, PhD Student Molecular Biophysics Center for Chemistry and Chemical Engineering Getingevagen 60 Lund University P.O.B. 124 SE-22100 Lund SWEDEN Tel: +46462224513
